Sealed off, fine focus, long life, flash x-ray tube



1955 E. L. CRISCUOLO ET AL ,7

SEALED OFF, FINE FOCUS, LONG LIFE, FLASH X-RAY TUBE Filed June 25, 1952Dn W60 mwm EGO W6 IRQO C LT D %L A w O E D R. W ATTORNEYS United StatesPatent (SEALED OFF, Focus, LONG LIFE, FLASH X-RAY TUBE Edward L.Criscnolo, Silver Spring, and Donald T. OConnor, Laurel, Md., assignorsto the United States of America as represented by the Secretary of theNavy The invention described herein may be manufactured and used by orfor the Government of the United States of America for governmentalpurposes without the payment of any royalties thereon or therefor.

This invention relates to flash X-ra'y tubes and more particularly to afine focus X ray tube of the sealed ofl, high vacuum type having a longtube life.

In the design of hash X-ray tubes, particularly those types which areused'in high speed radiography, it is desirable that the tube have afine focal spot to produce a welldefined image, that the tube be of thehigh vacuum Sealed ofi type to obviate the necessity for an elaboratevacuum pumping system to evacuate the tube, and that the tube possess alonglife. The tubes of the prior art have failed to meet one or more ofthese requirements. There are presently available X-ray tubes which aresealed oil but which produce a large focal spot due to the type ofanode'used, and which consequently result in the production of an imagelacking the requisite sharpness necessary in high speed flashradiography. There have also been attempts to produce a fine focus flashtube, but in the past these tubes have' not been of the sealed off typeand have thus required a vacuum pumping arrangement for continuallyevacuating the tube in order to remove vaporized tungsten which isemitted from the tungsten target at high temperatures to thereby preventaccumulation of a tungsten layer on'the inner surface of the X-ray tube.The deposit of tungsten on the window through which the X-rays areemitted reduces the intensity of the X-ray and thus shortens the life ofthe tube, and the deposit of large amounts of vaporized tungsten on theinner walls of the tube considerably decreases the internal resistanceof the tube and may eventually result in a short circuit between theanode and Cathode through the deposited tungsten coating. The resentinvention overcomes these difiiculties by providin a sealed off, highvacuum tube utilizing a target consisting of a tungsten cone forproducing a fine focus. A cylindrical shie'ld on which the vaporizedtungsten is collected is provided for the cathode to prevent theaccumulation of a tungsten layer on the inner Walls of the tube and onthe X-ray window.

Accordingly, it is an object ofthe present invention to provide a harshX-ray'tube of the high vacuum sealed off type using a comically shapedtarget to produce a fine focus.

Another object is to provide a fine focus flash tube which requires noexternal evacuating equipment.

A further object is to provide a shield for preventing the deposit of alayer of vaporized target material on the inner walls of the tube tothus prevent internal shorting.

A still further object is to provide a shield which reduces thedeposition of vaporized target material on the X-ray window to maintaina high X-ray intensity throughout the long life of the tube.

Further objects and many of the attendant advantages of this inventionwill be readily appreciated as the same 2,720,607 Patented Oct. 11, 1955becomes better understood by reference to the following detaileddescription when considered in connection with the accompanying drawingwherein:

Fig. 1 illustrates one embodiment of the X-ray tube showing a crosssectional view taken along a plane passed longitudinally through thetube;

Fig. 2 shows a transverse cross-sectional view of the tube taken along aline corresponding substantially with line 2-2 of Fig. l; and

Fig. 3 shows a transverse cross-sectional view of the tube taken along aline corresponding substantially with line 3-3 of Fig. 1.

Referring now to the drawing, wherein like reference charactersdesignate like or corresponding parts throughout the several views,there is shown in Fig. 1 (which illustrates a preferred embodiment) aglass envelope 10 for the X-ray tube which is provided with a re-entrantportion 11 at the rear thereof and an X-ray Window 12 at the front.Extending along the longitudinal axis of the tube and protruding beyondthe rear portion is a conducting rod 13, which may be made of Kovar,Fernico, German silver, or the like, these materials being chosen sincetheir temperature coefficient of expansion is substantially the same asthat of glass to thus enable a seal to be maintained between theconducting rod and the reentrant portion 11 of the glass envelope with achange in temperature.

Secured to the front portion of the conducting rod 13 is a conieallyshaped target 14 in which the axis of the cone extends along thelongitudinal axis of the tube and the base of the cone abuts the frontportion of the conducting rod. The cone may be secured to the rod bymeans of a weld of stainless steel, nickel, or the like, or may beattached in other suitable manner. It is contemplated that the target hemade of tungsten. However, other materials having a high melting pointand a high atomic number which provide a substantial quantity of X-rayswhen bombarded with electrons, may be used.

Extending through the front face of the tube are a pair of conductinglead wires 16 and 17 which may be made of Kovar, German silver, or othermaterials having properties similar to those of the conducting rod 13 soas to maintain a seal between the glass envelope and the lead wires uponchange in temperature. The lead wire 17 is connected to an annular platecathode 18 which is positioned perpendicular to the longitudinal axis ofthe tube so that this axis passes through the center of the aperture inthe plate and the apex of the conical target 14 is positioned atapproximately the center of the aperture in the plate. The lead Wire 16is connected to a cathode disc 19 having a flared portion 20 and acentral opening through the flared portion of approximately the samediameter as the aperture in the annular plate 18. The disc 19 ispositioned parallel to the plate 18 so that the central opening of theflared portion and the aperture in the plate are alined and so that asmall space exists between the edge of the flared portion 20 and theplate 18. This spaced relationship is maintained by a plurality ofinsulating glass beads which are secured to the lead wires 16 and 17 andwhich are positioned in spaced relationship around the plate 18 and thedisc 19 within the tube. A cylindrical sleeve 22 is secured to the outeredge of the plate 18 in any suitable manner, such as by welding the tabs21 to the plate, whereby the sleeve extends rearwardly from the plate soas to encircle the conical target 14 and a portion of the conducting rod13. A hollow shield 24 is affixed to the disc 19 in any suitable manner,such as by welding the tabs 23' to the disc, so that the shield extendsforwardly from the disc to a position near the X-ray window 12.

A positive high voltage of approximately kilovolts is impressed on thetarget 14 from a suitable source, for

' electrons emanated from the cathode.

instance, from a charged capacitor system well known in the prior artand disclosed in United States Patent 2,311,705 to C. M. Slack. In amanner similar to that shown by Slack, the leads 16 and 17 of thepresent tube may be connected to a pulse transformer whereby a pulse isapplied across the cathode gap between the plate 18 and the flaredportion 20 at a predetermined instant.

The charged capacitor may then. discharge along the conducting rod' 13,the target anode. 14, and through the tube to the cathode atgroundpotential. The spark across the cathode gap developed between theplate 18 and the flared portion 20 causes the cathode, which may be madeof tantalum, stainless steel, brass, or other such materials which donot evolve gasses under bombardment and which consequently areserviceable in a vacuum, toemit electrons which are directed towards thetarget 14; The target 14, the temperature of which has beencouside'rablyraised by the high voltage discharge focal point will'result, whereas ifthe target is moved.

rearwardly of the plate 18 eventually a point is reached in which thespacing between the target and the cathode is too great and aninsuificient supply of'X-rays is produced. Therefore,'the positioning ofthe target with respect to' the cathode. will be determined by the sizeof the focal spot desired and by the maximum spacing which may occurbetween the target and the cathode to attain the requisite X-rayintensity.

' .The bombardment'of the apex of the target 14 by electrons from thecathode plate 18 and the cathode disc '19 causes X-rays to be emittedfrom theapex of the cone which are directed along the longitudinal axisof the tube toward the X-ray window. During the high voltage dischargefrom the target to the cathode, the tungsten target is heated above itsmelting point, vaporizing a portion of the tungsten. Were it not for thepresence of the sleeve 22 and the shield 24 this vaporized tungstenwould 'be deposited on the inner walls of the envelope and f'there-entrant portion 11 to eventually cause a short of these shields andthus prevents the accumulation of a tungsten deposit on the'innersurface of the envelope 10. The'shield 24 also aids in preventing thedeposition of vaporized tungsten on the inner surface of the X-raywindow 12. If a tungsten layer is deposited on the X- ray window, theX-ray intensity of the tube will be considerably diminished inasmuch'astungsten is a very dense material which inhibits the passage of X-raystherethrough. The shield 24,'however, collects a large portionof thevaporized tungsten which would otherwise be'deposited on the X-raywindow. Due to the high pocenter point of'the aperture of thesecondplate is also.

Use of the sleeve 22 and the shield 24 causes V,

V 4 angles may be used, since a smaller angle cone produces an evenfiner focus and a larger angle cone yields a somewhat larger focal spot.

Obviously many modifications and variations of. the

present invention are possible in the light of the'above teachings. Itis therefore to be understood that within the. scope of the appendedclaims the invention may be practiced otherwise than as described.

What is claimed is: i

1. In combination, a high vacuum sealed off X-ray tube, a conductingmember extending longitudinally of the tube, a conically shaped targetsecured to said conducting member, a first apertured cathode platepositioned so that the apex of the cone is located at approximately thecenter of the aperture in the plane of said first plate, and a secondapertured cathode plate positioned parallel to said first plate so thatthe apertures in the first and second plates are alined whereby X-raysare produced from the target through the alined apertures to a finefocal point when the. target is bombarded by electrons from the cathode.j

2. In combination, a high vacuum' sealed off. X-ray tube, a conductingmember extending longitudinally of the tube, a conically shaped targetsecured to saidcon point of the aperture is'located on the longitudinalaxis of the tube and the plate is positioned near the apex of the cone,and a second apertured cathode plate'in par-- allel spaced position fromthe first plate so that the located on the longitudinal axis 'of. thetube whereby X-rays are emitted from the target directed along thelongitudinal axis of the tube to a fine focal point when the target isbombarded by electrons from the cathode.

3. A fine focus flash X-ray tube comprising, a high vacuum sealed 'ofienvelope, a pair of spaced circular apertured cathode plates, ,a pointedconically shaped target for producing X-rays having .a fine focal pointwhen bombarded by electrons from the cathode, the apertures of saidcathode plates and the axis of said target being aligned along thelongitudinal axis of said tube, and means for collecting vaporizedtarget material:to prevent deposition of the target material on theinner walls of the envelope to thereby provide ta long life X-ray tube.

4. A fine focus flash X-ray tube comprising,.a high vacuum sealed offenvelope, a pair of spaced circular apertured cathode plates, a pointedconically shaped of said cathode plates and the axis of said targetbeing" aligned along the longitudinal axis of said tube, meanssurrounding the target and extending rearwardly thereof .for collectingvaporized target material and prevent its tential gradient which existsbetween the cathode and the target at the instantthe tube is flashed andfor a short period thereafter, the vaporized tungsten which is producedat the target is directed towards the cathode and the cathode shield.Therefore, nearly all of the vaporized deposition on the inner walls ofthe envelope, and means extending forwardly of the target in'thedirection of X-ray emission for preventing deposition of vaporizedtarget material on the surface "of the envelope through which the X-raysare emitted. V I a r 5. A fine focus flash X-ray tube comprising a highvacuum sealed off envelope, an X-ray window in the envelopes surface, anapertured cathode plate, a pointed conically shaped target having theapex thereof positioned substantially at the center of the cathodeaperture for i producing X-rays having a fine focal spot whenbombarded'by electrons from the cathode, the center of the aperture ofsaid cathode and the axis'of said target being aligned along thelongitudinal 'axis of said tube, and a hollow shield extending forwardlyof the cathode toward the X-ray window in the direction of emission ofX-rays from the target so as to prevent the accumulation of vaporizedtarget material on the X-ray window to thereby produce a' tube having along life and high X-r'ay intensity.

6. A fine focus flash X-ray tube comprising a high vacuum sealed offenvelope, an Xn'ay window in the envelope surface, an apertured cathodeplate, a pointed conically shaped target having the apex positionedsubstantially at the center of the cathode aperture for producing X-rayshaving a fine focal spot when bombarded by electrons from the cathode,the center of the aperture of said cathode and the axis of said targetbeing aligned along the longitudinal axis of said tube, and a pair ofcylindrical shields one of which extends rearwardly from the apex of theconical target to surround the target and the other of which extendsforwardly of the apex of the target toward the X-ray window to preventdeposition of vaporized target material on the inner surface of thewalls of the envelope and on the surface of the X-ray window to therebyproduce a tube having a long life and high X-ray intensity.

7. A fine focus flash X-ray tube comprising a high vacuum sealed Eenvelope, an apertured cathode plate, a conducting member extendingalong the longitudinal axis of the envelope, a pointed conically shapedtarget secured to the conducting member, said target having the apexpositioned substantially at the center of the cathode aperture so thatthe center of the aperture of said cathode and the axis of said targetare aligned along the longitudinal axis of said tube causing X-rays tobe directed from the apex of the conical target along the longitudinalaxis of the envelope to produce a fine focal point when the target isbombarded by electrons from the cathode, and a cylindrical shieldsurrounding the target and a portion of the conducting member so thatthe axis of the cylindrical shield coincides with the longitudinal axisof the envelope whereby the deposition of vaporized target material onthe inner surface of the envelope walls is prevented.

8. A fine focus flash X-ray tube comprising a high vacuum sealed offenvelope, a pointed conically shaped target for producing X-rays, a pairof spaced apertured cathode plates positioned so that the apex of thecone is positioned at approximately the center of the aperture in theplane of the first cathode plate whereby the target is bombarded byelectrons from the cathode plates to produce the X-rays, and a shieldsecured to the cathode plates so as to surround the target and preventthe accumulation of the deposited target material on the inner surfaceof the walls of the envelope.

9. A fine focus flash X-ray tube comprising a high vacuum sealed offenvelope, a conducting member extending longitudinally of the envelope,a pointed conically shaped target secured to said conducting memberwithin the envelope for producing X-rays, a pair of spaced aperturedcathode plates positioned so that apex of the cone is located atapproximately the center of the aperture in the plane of the firstcathode plate whereby the target is bombarded by electrons from thecathode plates to produce X-rays, and a cylindrical shield, the axis ofwhich coincides with the longitudinal axis of the envelope secured tosaid cathode plates and surrounding the target and a portion of saidconducting member so that the deposition of vaporized target material onthe inner walls of the envelope is prevented.

10. In combination, a high vacuum sealed off X-ray tube, a conicallyshaped target, a pair of spaced apertured cathode members positioned sothat apertures are alined and the axis of the conical target coincideswith the center line of the alined apertures whereby X-rays are directedalong the center line to a fine focal point when the target is bombardedby electrons from the cathode, a hollow sleeve attached to one of saidcathode members so as to surround the target, and a hollow shieldsecured to the other to said cathode members and extending in thedirection of the emission of the X-rays, said shield and said sleeveserving to prevent the deposition of vaporized target material on theinner surface of the walls of the tube.

11. In combination, a high vacuum sealed off X-ray tube, an X-ray windowin the tube surface, a conically shaped target for producing X-rays, apair of spaced apertured cathode members positioned so that theapertures are alined and the axis of the conical target coincides withthe center line of the alined apertures whereby X-rays are directedalong the center line to a fine focal point when the target is bombardedby electrons from the cathode, a hollow sleeve secured to one of saidcathode members so as to surround the target, and a hollow cylindricalshield secured to the other of said cathode members and extending towardthe X-ray window to collect vaporized target material and prevent itsdeposition on the surface of the X-ray window whereby a long life X-raytube having a high X-ray intensity is produced.

12. In combination, a high vacuum sealed off X-ray tube, an X-ray windowin the tube surface, a conducting member extending longitudinally of thetube, a conically shaped target secured to said conducting member withinthe tube so that the axis of the cone coincides with the longitudinalaxis of the tube, a first apertured cathode plate positioned so that thecenter point of the aperture is located on the longitudinal axis of thetube and the plate is positioned near the apex of the cone, a secondapertured cathode plate in spaced position from the first plate so thatthe center point of the aperture of the second plate is also located onthe longitudinal axis of the tube whereby X-rays which are emitted fromthe target upon bombardment by electrons from the cathode are directedalong the longitudinal axis of the tube to a fine focal point, a hollowsleeve secured to the first plate so as to surround the target and aportion of the conducting member, and a cylindrical shield secured tosaid second cathode plate and extending towards the X-ray window in thedirection of emission of the X-rays so as to collect vaporized targetmaterial and prevent deposition of that material on the surface of theX-ray window and the inner surface of the tube.

13. In combination, a high vacuum sealed off X-ray tube, an X-ray windowin the tube surface, a conducting member extending along thelongitudinal axis of the tube, an X-ray producing target secured to saidconducting member, a first cathode plate positioned near the target sothat the plane of the plate is perpendicular to the longitudinal axis ofthe tube, a second cathode plate positioned parallel to the first platewith a slight space between the plates, a first conducting shieldsecured to the first plate so as to surround the target and a portion ofthe conducting member to prevent the deposition of vaporized targetmaterial on the inner walls of the tubes, and a second conducting shieldsecured to the second plate and extending towards the X-ray window inthe direction of the emission of X-rays from the target to prevent thedeposition of target material on the Window.

14. In combination, a high vacuum sealed off X-ray tube, an X-ray Windowin the tube surface, a conducting rod extending along the longitudinalaxis of the tube, an X-ray producing target secured to said conductingrod, a first apertured cathode plate positioned near the target so thatthe plane of the plate is perpendicular to the longitudinal axis of thetube, a second apertured cathode plate positioned parallel to the firstplate with a slight gap between the two, a first cylindrical shieldsecured to the first plate so as to surround the target and a portion ofthe conducting rod to prevent the deposition of target material on theinner Wall of the tube, and a second cylindrical shield secured to thesecond plate and extending towards the X-ray window in the direction ofemission of X-rays from the target so that the X-rays pass from thetarget through the apertures in the two plates and through the secondcylindrical shield to the X-ray window, said shields serving to preventthe deposition Refel ences Cited in the file of this patent UNITEDSTATES PATENTS Holst et a1. July 6, 19 26 Lilienfeld Feb. 8, 1927 Holstet a1 June 14, 1927 Forde Mar. 6, 1934 Bouwers Sept. 25, 1934 Huppertetal. Sept. 8, 1936 Cassen Aug. 4, 1942 Atlee Aug. 24, 1943 De GraafOct. 31, 1944

